1. Field of the Invention
The invention relates a method of bonding diamond heat sinks to adjacent structures to support slow wave electromagnetic energy propagating structures.
2. Description of the Prior Art
Traveling wave electron discharge devices typically incorporate a slow wave electromagnetic energy propagating circuit comprising a plurality of spaced periodic metallic members. The helix exemplifies one such a structure for propagating and amplifying electromagnetic energy by extracting kinetic energy from an adjacent high power electron beam. The high frequency energy travels along the slow wave structure at a velocity less than that of light and a synchronous relationship is established to provide for interaction between the electrons in the beam and the waves on the slow wave structure. Electric and magnetic fields of the traveling electromagnetic energy induce perturbations in the electron beam to form electron packets or bunches and space charge waves as a result of the net exchange of energy. The electron beam becomes velocity and density modulated along the direction of trajectory to produce alternating high frequency energy in either the backward or forward wave mode. The slow wave structure due to ohmic losses as well as electron bombardment becomes heated and a considerable amount of thermal energy must be dissipated from such structures. Such thermal energy dissipation is required in order to attain higher average power levels in the electron interaction devices. This requirement is most significant at higher microwave energy frequencies where the physical dimensions of the slow wave guiding structure are relatively small which results in an overall increase in the thermal impedances. Typically, prior art devices utilize slow wave structure supports of nonelectrically conductive materials such as beryllia, boron nitride or ceramic having high thermal conductivity characteristics. Such materials are conventionally provided as elongated rods contacting the periodic components and extending parallel to the longitudinal axis of the device.
In accordance with U.S. Pat. No. 3,778,665 issued to R. Harper et al Dec. 11, 1973 and assigned to the assignee of the present invention, a means for reduction of the thermal impedances and increasing the thermal energy dissipation properties is disclosed utilizing spaced diamond heat sink support structures individually contacting the slow wave helix turns. The dielectric constant of diamonds is approximately 5.58 which is lower than beryllia and, therefore, low dielectric loading of the overall structure is attained together with the high thermal conductivity. The thermal conductivity of several types of natural diamonds are in the range of from 9 watts/.degree.C/cm to about 26 watts/.degree.C/cm. In the embodiment shown in the referenced patent diamond heat sink support structures are bonded or supported under compression at one end between metallic support rods and the inner walls of the envelope of the device. The other end contacts the turns of the helix slow wave structure. Further thermal energy dissipation means include the circulation of a fluid coolant adjacent the metallic supports for the diamond heat sink members. In an exemplary embodiment of the diamond supported helix slow wave structure shown in the referenced patent, and FIG. 4 of the drawings, the diamond heat sink supports provided approximately a sevenfold increase in thermal energy dissipation characteristics over prior art structures.
In FIG. 4 the prior art slow wave energy propagating structure comprises a helix delay line 10 having a plurality of turns 12. A conventional traveling tube device is provided with an electron gun including an emissive cathode adjacent to one end of the slow wave structure, as well as external magnetic field producing means and a collector electrode, together with the coaxial transmission line input and output means. These components have not been illustrated since they are believed to be well known in the art. A plurality of diamond heat sink supports 14 having a substantially flat planar surface 16, as illustrated in FIG. 3, contact turns 12 at spaced intervals approximately 90.degree. apart. Commercial grades of gem quality natural diamonds have thermal conductivity properties varying from 10 to 30 watts/.degree.C/cm. Each of the diamonds is joined by metallurgical techniques to rod members 18. The rod members in turn abut the outer ends of elongated hollow conduit members 20 such as blowpipes which in turn abut the metallic envelope 22. The referenced components are maintained within the tube envelope by means of a backwall member 24 of a highly conductive metal such as copper provided with spaced holes 26 to accommodate and radially support the rod members 18. Each of the blowpipe conduits 20 may be provided with a substantially flat planar surface 28 to abut against the rod members 18.
The prior art teachings required the metallizing of the diamond support members by a coating of sputtered titanium followed by sputtered platinum and then by a plating of gold. The rod members to which the diamond heat sinks are joined are also gold plated. It is also possible to braze the components with silver-copper eutectic alloy with 12 percent titanium by weight. These metallizing procedures are lengthy and expensive, however, since the end results are of such magnitude, the costs have been borne up to the present time.
It is an object of the present invention to provide a new and improved method for the bonding of diamond heat sink insulator supports for a slow wave structure.